Among aliphatic polyesters considered to give little load to the natural environment due to their biodegradability or hydrolyzability, polyglycolic acid resin has a particularly extensive decomposability, is excellent in mechanical strengths such as tensile strength and in gas-barrier property when formed into a film or sheet, and is therefore expected to be used as fishery materials, such as fishing yarns, fishery nets and culturing nets, agricultural material, or various packaging (container) materials (e.g., Patent documents 1-3 listed below). However, the severe hygroscopicity and hydrolyzability of polyglycolic acid resin have frequently provided a factor of obstructing the application thereof. For example, in the case of obtaining various forms, such as filament, film and sheet, an ordinary thermoplastic resin is generally melted, cooled, solidified and pelletized to obtain a particulate forming resin material, which is then supplied for various forming processes. This also holds true with polyglycolic acid resin but, as for polyglycolic acid resin having severe hygroscopicity (i.e., moisture absorptivity) and hydrolyzability, the resin is liable to cause lowerings of molecular weight and thus melt viscosity directly affecting the melt-formability due to hydrolysis thereof until it is subjected to various (melt-) forming processes during drying and storage after the polymerization, thus failing to exhibit desired formability in some cases. This is problematic even in the forming of polyglycolic acid resin alone but particularly in the forming of a composite material such as a laminate product with another thermoplastic resin as by co-extrusion. This is because an adjustment of formability can be performed without serious difficulty by adjusting melt-viscosity through an adjustment of melt-forming temperature, etc. in the case of forming of polyglycolic acid resin alone, whereas in the case of forming a composite material with another thermoplastic resin, the forming conditions cannot be freely changed corresponding to the change in melt-viscosity of the polyglycolic acid resin, thus being liable to result in product defects such as a change in relative thickness or a thickness irregularity of a laminate product.    Patent document 1: WO2003/037956A1    Patent document 2: JP10-60136A    Patent document 3: WO2005/072944A1